filterx: add E2E test for set_fields()

Signed-off-by: Attila Szakacs <attila.szakacs@axoflow.com>

tests/light/functional_tests/filterx/test_filterx.py

@@ -2520,3 +2520,33 @@ def test_proper_generation_counter(config, syslog_ng):
     assert "processed" in file_true.get_stats()
     assert file_true.get_stats()["processed"] == 1
     assert file_true.read_log() == '{"from_nvtable":"almafa","from_a_macro":"2000-01-01T00:00:00+01:00","unset_then_set":"kortefa"}\n'
+
+
+def test_set_fields(config, syslog_ng):
+    (file_true, file_false) = create_config(
+        config, r"""
+    $MSG = {
+        "foo": "foo_exists",
+        "bar": "bar_exists",
+    };
+    set_fields(
+        $MSG,
+        overrides={
+            "foo": [invalid_expr, "foo_override"],
+            "baz": "baz_override",
+            "almafa": [invalid_expr_1, null],  # Should not have any effect, as there is no valid expr or non-null here.
+        },
+        defaults={
+            "foo": [invalid_expr, "foo_default"],  # Should not have any effect, "foo" is handled by overrides.
+            "bar": "bar_default",  # Should not have any effect, "bar" already has value in the dict.
+            "almafa": "almafa_default",
+            "kortefa": [invalid_expr_1, null],  # Should not have any effect, as there is no valid expr or non-null here.
+        }
+    );
+    """,
+    )
+    syslog_ng.start(config)
+
+    assert file_true.get_stats()["processed"] == 1
+    assert "processed" not in file_false.get_stats()
+    assert file_true.read_log() == '{"foo":"foo_override","bar":"bar_exists","baz":"baz_override","almafa":"almafa_default"}\n'